A variety of susceptors have been previously proposed for absorbing microwave energy and transmitting it by conduction to crisp and brown the surface of the food product. Some prior susceptors were stiff, brittle, subject to breakage or otherwise unsuited for use in lightweight, disposable and low cost packaging. In other cases the susceptor, while interacting with the microwave energy present in an oven, does not adequately heat or crisp the food product. Other susceptors heat only one side of the food product. So, for example, if the food product is rectangular in shape, two or three sides remain pale and uncrispened. The susceptor itself should be easy to insert into the package and be held securely in place. The hot package should also be easy to remove from the oven without burning the fingers.
It has been found that when a food product such as a french fried potato is placed in an ordinary paper carton and heated in a microwave oven, the potato becomes soggy. This occurs even if an effort is made to allow steam to escape through openings at the top of the package. As a result, attempts have been made to develop a more effective susceptor for lining food cartons to augment the heat provided by direct microwave interaction with the food. For example, U.S. Pat. Nos. 4,612,431 and 4,735,513 describe a susceptor formed from polyester film to which a thin, semiconductive layer of metal is applied. These laminates are bonded, for example, to two opposing walls of the package for absorbing microwave energy and then transfering it to the food product. Tests conducted in the development of the present invention show, however, that these laminates and the resulting packages are not effective in crisping, browning or toasting the surface of a food such as a french fried potato. After heating, the product still tends to be perceived as somewhat moist, limp and soggy. A major objective of the invention is therefore to provide a microwave susceptor package that will crisp, toast or brown several surfaces of a stick-shaped food product such as french fried potatoes, fish sticks or the like so that the food is perceived to be crisp and appetizing to the consumer.
Other attempts have been made to deal with this problem. For example, U.S. Pat. Nos. 4,267,420 and 4,230,924 provide a lightweight flexible wrapper formed from a laminate composed of a flexible sheet material that interacts with microwave energy. One major shortcoming is that the food sticks have to be individually wrapped and later unwrapped one-by-one by the customer. Another problem results from the fact that portions of the sheet material will shrivel, shrink, split and crack, particularly in areas where it is folded or not in contact with the food.